Referring to FIG. 1, a typical upright vacuum cleaner 100 includes a base 102 that is configured to move along a surface such as a floor, and an upper housing 104 that usually is pivotally mounted to the base 102 and provided with a grip 106 that is used to manipulate and maneuver the device. The downward-facing surface of the base 102 includes a main suction inlet that faces the floor, and through which dirt-laden air is drawn into the device by a motor-driven vacuum fan 108. The vacuum fan 108 may be located in the upper housing 104, as shown, or in the base 102. The main inlet and vacuum fan 108 are in fluid communication by one or more ducts and flexible hoses that collectively form a flow path through the vacuum cleaner 100, as well-known in the art. Ultimately, the air exits the flow path through an outlet to the ambient air. Any number of filtration devices, such as screens, pleated filters, foam filters, and cyclonic separators may be included in the flow path, either upstream or downstream of the vacuum fan 108. For example, the upright vacuum cleaner 100 may have a dirt separation device 110, such as a bag filter or cyclone chamber, located in the upper housing 104. The dirt separation device 110 may alternatively be located in the base 102. Examples of full-size and smaller “stick” upright vacuum cleaners having these and other features are provided in U.S. Pat. Nos. 6,829,804; 7,163,568; 7,228,592; 7,293,326; 7,662,200; 7,814,612; and 8,572,801, which are incorporated herein by reference.
A typical canister vacuum cleaner 200, such as the one shown in FIG. 2, has a canister body 202 that is connected to a cleaning head 204 by a flexible hose 206 and rigid pipe 208. The pipe 208 often has a grip 210 for manipulating the cleaning head 204. The lower surface of the cleaning head 204 has a suction inlet that is fluidly connected, through the pipe 208 and hose 206, to a vacuum fan (not shown) located inside the canister body 202. As with an upright vacuum cleaner, the canister vacuum cleaner 200 has a flow path in which one or more filtration devices 212 are located. The filtration device 212 usually is in the canister body 202. It is also known to add auxiliary filtration devices, such as a small cyclone separator, to the pipe 208 or cleaning head 204. Examples of canister vacuum cleaners include U.S. Pat. Nos. 3,745,965; 4,953,253; 6,168,641; 6,502,277 and 7,951,214, which are incorporated herein by reference. A variation on a canister vacuum cleaner is a central vacuum, which uses a fixed cleaning module in one room of a house, and remote cleaning head ports in various rooms in the house. An example of such a device is shown in U.S. Pat. No. 4,829,626, which is incorporated herein by reference.
In some instances, the main inlet may be adjustable to space it at different heights relative to the surface being cleaned. Various vacuum cleaners having inlet height adjustment devices have been produced in the prior art. In many cases, the height adjustment device includes a carriage to raise and lower the front portion of a vacuum nozzle to regulate the height of a brushroll located inside the nozzle housing relative to the surface being cleaned. Such devices often are user-actuated by a foot pedal that engages a camming mechanism, but it is also known to use electronically or hand-operated devices. Examples of such a devices are shown in U.S. Pat. Nos. 4,167,801; 4,437,205; 4,467,495; 5,134,750; 5,609,024; 6,081,963; 7,246,407; 7,266,861; 7,293,326; and 7,945,988, which are incorporated herein by reference.
When cleaning some surfaces, the suction generated by the vacuum cleaner can draw portions of the surface (e.g., fibers of a carpet) near or into the suction inlet opening, decreasing the circulation of airflow and increasing negative pressure inside the vacuum cleaner airflow passages. This increased negative pressure can pull the vacuum cleaner head and the surface being cleaned together, causing a phenomenon (sometimes called “suction lock”) that prevents easy movement of the cleaning head across the surface being cleaned. This condition can also prevent proper airflow across the suction fan motor, resulting in motor overheating.
Air bypass (i.e., “bleed”) openings are often included in vacuum cleaner air paths to release negative pressure in the suction path, and increase the circulation of airflow even when the main inlet is very close or contacting the surface being cleaned. Such bypass openings can be positioned in various locations of vacuum cleaners. For example, some vacuum cleaners include a simple hole located within the body of the vacuum cleaner near the suction fan inlet, while others use unsealed seams at locations such as the cover over a vacuum bag chamber to discreetly allow air to continue to flow through the suction fan even if the normal cleaning inlet is blocked. Other devices have bypass openings located in the upper or side surfaces of the base 102 or cleaning head 204. Still other devices include slots around the perimeter of the suction inlet to provide tunnels to allow airflow even if the suction inlet is pressed flat against a surface. It is also known to provide vacuum cleaners with bleed valves to release pressure within the vacuum cleaner. For example, in some cases, a bypass opening is covered by a valve that opens when the pressure differential between the suction path and the outside air is great enough to overcome a spring or other device that normally holds the valve closed (i.e., a “bleed valve” or “pressure relief valve”). Examples of such devices are shown, for example, in U.S. Pat. Nos. 2,904,816; 2,904,817; and 6,018,845, which are incorporated herein by reference. While some known bleed openings and bleed valves may be helpful to avoid or reduce suction lock, in many cases they are provided primarily for other reasons, such as to prevent motor overheating.
There exists a need for improved pressure relieving mechanisms in cleaning heads of vacuum cleaners to prevent or reduce suction lock and allow for easy movement of the cleaning heads across cleaning surfaces.